An optical add-drop multiplexer (OADM) node comprises a collection of optical and control devices used in wavelength-division multiplexing systems for multiplexing and routing different channels of light into or out of, e.g., one or more multiple single mode fibers (SMFs). The terms “add” and “drop” in the context of an OADM node refer to the capability of the OADM node to add one or more new wavelengths, channels or colors to an existing multi-wavelength wavelength division multiplexed (WDM) or dense WDM (DWDM) signal, and/or to drop (remove) one or more channels from the WDM or DWDM signal. An OADM node may be considered to be a specific type of optical cross-connect.
A reconfigurable OADM (ROADM) node is a form of OADM node that includes the ability to remotely switch or control traffic in a DWDM system, e.g., via software control (whereas OADM nodes are considered to have fixed add/drop capabilities with respect to, e.g., colors or direction). As such, a ROADM node enables increased flexibility in network transport by allowing a telecommunications provider to add or drop any channel, under remote control. In this way, a ROADM node allows for very flexible, remote selection and routing of wavelengths transiting a given node on a fiber network. Similarly, a ROADM node may also allow flexible access to any of the wavelengths going through the node for use of the data on the chosen wavelength and the possibility of adding to, or modifying, the data on that wavelength for transmitting it on to the next node(s). A ROADM node may also allow the interconnection of multiple intersecting networks (multiple degree nodes) at the optical level, avoiding the expense and complexity of optical-electrical-optical conversions to achieve the interconnection. Thus, as the demand in a given network changes, additional or different channels can be dropped or added, under remote control, creating a flexible optical network provisioning system.